I have a 1000-UP, Serial number 5213-25-291. I removed the bad thermostat and it is a Robertshaw Z-87147-36, MT 200, Type B-10.

The only difference I see with this TT-33432-B10 thermostat is that the capillary tube is 84", most likely for the double unit with top mounted controls. Mine has the controls above each section so it doesn't necessarily need to be that long.

Also does the control knob come with this thermostat as shown in the photo? Mine are cracked and wiped clean with no markings.